DDR2 667 MHz SDRAM, 2 x SODIMM socket for expansion up to 4GB SDRAM*Due to the 32-bit operation system's limitation, only 3GB will show up with a 4GB memory. The 64-bit operating system will not have this issue. For more information, please check Microsoft's support site: http://support.microsoft.com/kb/946003Intel® Turbo Memory Technology with 1GB NAND Flash(optional)